1. Field of the Invention
The present invention relates to the recovery of rare earth values from gypsum.
2. Description of the Prior Art
The rare earths, which are elements constituting the lanthanide group of the Periodic Table of Mendeleev, are present in many natural ores at more or less high concentrations.
In the following description, by the expression "rare earths" are intended the rare earth elements designated the lanthanides and having atomic numbers ranging from 57 to 71, inclusive, as well as yttrium which has an atomic number of 39.
Many processes for the recovery of rare earths from ores containing high, medium or even low contents of rare earth values are known to this art.
However, these processes do not permit using all existing ores or sources of rare earths as suitable starting materials.
Indeed, the rare earths are likewise present in natural minerals or in residues emanating from processes for the treatment of an ore for the purpose of extraction or the production of other compounds, such as gypsums.
Given the significant amounts of gypsum available worldwide, many efforts have to date been made to recover the rare earth values contained in this material.
Nonetheless, all of the hitherto known processes do not permit the economic recovery of the rare earths. In particular, their degrees of recovery are quite low.